Nicotinamide adenine dinucleotide (NAD) and its derivative compounds are known as essential coenzymes in cellular redox reactions in all living organisms. Several lines of evidence have also shown that NAD participates in a number of important signaling pathways in mammalian cells, including poly(ADP-ribosyl)ation in DNA repair (Menissier de Murcia et al., EMBO J., (2003) 22, 2255-2263), mono-ADP-ribosylation in the immune response and G protein-coupled signaling (Corda and Di Girolamo, EMBO J., (2003) 22, 1953-8), and the synthesis of cyclic ADP-ribose and nicotinate adenine dinucleotide phosphate (NAADP) in intracellular calcium signaling (Lee, Annu. Rev. Pharmacol. Toxicol., (2001) 41, 317-345). Recently, it has also been shown that NAD and its derivatives play an important role in transcriptional regulation (Lin and Guarente, Curr. Opin. Cell. Biol., (2003) 15, 241-246). In particular, the discovery of Sir2 NAD-dependent deacetylase activity (e.g., Imai et al., Nature, (2000) 403, 795-800; Landry et al., Biochem. Biophys. Res. Commun., (2000) 278, 685-690; Smith et al., Proc. Natl. Acad. Sci. USA, (2000) 97, 6658-6663) drew attention to this new role of NAD.
The Sir2 family of proteins consumes NAD for its deacetylase activity and regulates transcription by deacetylating histones and a number of other transcription regulators. Because of this absolute requirement for NAD, it has been proposed that Sir2 proteins function as energy sensors that convert the energy status of cells to the transcriptional regulatory status of genes (Imai et al., Nature, (2000) 403, 795-800; Imai et al., Cold Spring Harbor Symp. Quant. Biol., (2000) 65, 297-302). Sir2 proteins produce nicotinamide and O-acetyl-ADP-ribose in addition to the deacetylated protein substrates in their deacetylation reaction (Moazed, Curr. Opin. Cell. Biol., (2001) 13, 232-238; Denu, Trends Biochem. Sci., (2003) 28, 41-48; see also FIG. 1), and nicotinamide is eventually recycled into NAD biosynthesis. Unlike other NAD-dependent biochemical reactions, the NAD-dependent deacetylase activity of the Sir2 family of proteins is generally highly conserved from bacteria to mammals (Frye, Biochem. Biophys. Res. Commun., (2000) 273, 793-798), suggesting that the connection between NAD and Sir2 proteins is ancient and fundamental. In mammals, the Sir2 ortholog, Sirt1/Sir2α, has been shown to regulate metabolism in response to nutrient availability (Bordone and Guarente, Nat. Rev. Mol. Cell Biol., (2005) 6, 298-305). In adipocytes, Sirt1 triggers lipolysis and promotes free fatty acid mobilization by repressing PPAR-gamma, a nuclear receptor that promotes adipogenesis (Picard et al., Nature, (2004) 429, 771-776). In hepatocytes, Sirt1 regulates the gluconeogenic and glycolytic pathways in response to fasting by interacting with and deacetylating PGC-1α, a key transcriptional regulator of glucose production in the liver (Rodgers et al., Nature, (2005) 434, 113-118). Additionally, Sirt1 promotes insulin secretion in pancreatic beta cells in response to high glucose partly by repressing Ucp2 expression and increasing cellular ATP levels (Moynihan et al., Cell Metab., (2005) 2, 105-117). While little is known about the regulation of NAD biosynthesis in mammals, NAD biosynthesis may play a role in the regulation of metabolic responses by altering the activity of certain NAD-dependent enzymes such as Sirt1 in a variety of organs and/or tissues.
The NAD biosynthesis pathways have been characterized in prokaryotes by using Escherichia coli and Salmonella typhimurium (Penfound and Foster, Biosynthesis and recycling of NAD, in Escherichia coli and Salmonella: Cellular and Molecular Biology, p. 721-730, ed. Neidhardt, F. C., 1996, ASM Press: Washington, D.C.) and recently in yeast (Lin and Guarente, Curr. Opin. Cell. Biol., (2003) 15, 241-246; Denu, Trends Biochem. Sci., (2003) 28, 41-48). In prokaryotes and lower eukaryotes, NAD is synthesized by the de novo pathway via quinolinic acid and by the salvage pathway via nicotinic acid (Penfound and Foster, id.) In yeast, the de novo pathway begins with tryptophan, which is converted to nicotinic acid mononucleotide (NaMN) through six enzymatic steps and one non-enzymatic reaction (Lin and Guarente, Curr. Opin. Cell. Biol., (2003) 15, 241-246). Two genes, BNA1 and QPT1, have been characterized in this pathway in yeast. At the step of NaMN synthesis, the de novo pathway converges with the salvage pathway. The salvage pathway begins with the breakdown of NAD into nicotinamide and O-acetyl-ADP-ribose, which is mainly catalyzed by the Sir2 proteins in yeast. Nicotinamide is then deamidated to nicotinic acid by a nicotinamidase encoded by the PNC1 gene. Nicotinic acid phosphoribosyltransferase (Npt), encoded by the NPT1 gene, converts nicotinic acid to NaMN, which is eventually converted to NAD through the sequential reactions of nicotinamide/nicotinic acid mononucleotide adenylyltransferase (encoded by NMA1 and/or NMA2) and NAD synthetase (encoded by QNS1).
Many aspects of mammalian behavior and physiology are coordinated through interconnected networks of 24-hour central and peripheral oscillators that synchronize cycles of fuel storage and utilization to maintain organismal homeostasis. In mice, circadian disruption has been tied to metabolic disturbance (F. W. Turek et al., Science 308, 1043 (2005); R. D. Rudic et al., PLoS Biol. 2, e377 (2004)), while conversely, high-fat diet alters both behavioral and molecular rhythms (A. Kohsaka et al., Cell Metab. 6, 414 (2007); M. Barnea, Z. Madar, O. Froy, Endocrinology 150, 161 (2009)). The underlying mechanism of the mammalian clock consists of a transcription-translation feedback loop in which CLOCK and BMAL1 activate transcription of Cryptochrome (Cry 1 and 2) and Period (Per1, 2, and 3), leading to subsequent repression of CLOCK:BMAL1 by CRY and PER proteins (J. S. Takahashi, H. K. Hong, C. H. Ko, E. L. McDearmon, Nat. Rev. Genet. 9, 764 (2008)). An additional feedback loop involves the transcriptional regulation of Bmal1 by ROR□ and REV-ERB□ (N. Preitner et al., Cell 110, 251 (2002); T. K. Sato et al., Neuron 43, 527 (2004)). Previous studies have also implicated a role for cellular NAD+ in the regulation of CLOCK and NPAS2 activity (J. Rutter, M. Reick, L. C. Wu, S. L. McKnight, Science 293, 510 (2001)), an observation consistent with the recent finding that the NAD+-dependent protein deacetylase SIRT1 modulates activity of the clock complex (Y. Nakahata et al., Cell 134, 329 (2008); G. Asher et al., Cell 134, 317 (2008)).
U.S. Pat. No. 8,106,184 describes methods of manufacturing and using nicotinoyl riboside compositions.
U.S. application Ser. No. 11/396,359 describes nicotinamide riboside analogues and their uses.
U.S. application Ser. No. 11/053,185 describes methods and compositions for modulating the life span of eukaryotic and prokaryotic cells and for protecting cells against certain stresses, including modulating the flux of the NAD+ salvage pathway in the cell.
There remains a need for improved compositions and methods of using such compositions for pharmacologic intervention and/or manipulation of the NAD pathway in mammalian cells and tissues.